1. Field of the Invention
The present invention relates to shaping and tempering apertured glass sheets and, while it may be incorporated in a single glass sheet shaping mold, is particularly suitable to a method and apparatus that incorporates shaping glass sheets by a press bending operation that is capable of producing apertured bent glass sheets on a mass-production basis within precise toleances. Though the present invention originated to solve problems existing in the shaping and tempering of glass sheets, particularly sheets having a thickness of 4 mm or less, it is understood that the principles of the present invention may be employed for shaping apertured sheet material composed of heat-softenable compositions other than glass.
Glass sheets or plates have been bent by supporting the sheet to be bent between a pair of glass shaping molds while at a temperature sufficiently high to be deformable by pressurized contact between the pair of glass shaping molds having major, complementary shaping surfaces conforming to the shape desired for the bent glass. In the past, the glass shaping molds comprised either solid metal or refractory members or outline metal members covered with suitable material to insulate the glass from direct contact with the metal so as to avoid chill cracking.
Apertured glass sheets shaped by press bending using solid molds tended to develop flaws at the periphery of the apertures. Such flaws led to production losses.
If the apertured glass, while shaped by press bending molds, is contacted around its marginal portion only, only the shape of the marginal edge is controllable within tolerance. The shape of the interior portion is not controlled.
It would be beneficial for the glass sheet bending art to develop a method of conforming apertured glass sheets to their desired shape throughout their entire extent without introducing flaws in the vicinity of the glass sheet apertures that result in a high frequency of production losses during a bending and tempering operation, during which the apertured glass sheets are subjected to high temporary stresses.
2. Description of Patents of Interest
U.S. Pat. No. 3,367,764 to Seymour provides glass shaping apparatus of the press bending type that engages the opposite surfaces of the glass substantially equally during the shaping operation, that is easily adjustable to change its shape in the event glass is bent slightly out of tolerance without requiring dismantling of the entire apparatus, and that is capable of simple adjustment to produce several different configurations that are not too dissimilar from one another.
The Seymour patent provides apparatus for bending a heat-softened glass sheet by sandwiching a glass sheet in pressurized engagement between glass facing surfaces of a pair of glass shaping molds having major, complementary shaping surfaces conforming substantially to the shape desired for the bent glass sheet and relatively movable between a retracted position and a glass engaging position.
A glass shaping mold of the Seymour patent comprises a relatively flexible shaping plate of metal having a pressing face whose shape approximates that of the shape desired for the glass sheet after bending. The relatively flexible shaping plate extends substantially continuously throughout substantially its entire extent and has sufficient rigidity to resist deformation during pressurized engagement against a heat-softened glass sheet.
The apparatus also comprises a relatively rigid member in the form of a metal plate having an area at least substantially coextensive with that of the relatively flexible metal plate located in spaced relation behind said relatively flexible metal plate. Attachment means is distributed throughout the extent of the relatively flexible metal plate and the relatively rigid metal plate for connecting the plates in spaced relation to one another, for insuring positive alignment of the central portion of the shaping plate to the corresponding portion of the rigid plate while permitting the shaping plate to expand thermally without distorting from its desired local configuration, and for making slight alterations in the shape of the relatively flexible metal plate without altering the configuration of the relatively rigid metal plate. The space between the shaping plate and the rigid plate permits access to adjust the attachment means. Such adjustment changes the local contour of the shaping plate by altering the distance between the shaping plate and the rigid plate in the vicinity of the attachment means.
While the apparatus patented by Seymour is suitable for shaping glass sheets to different shapes, the adjustment members are arranged in a checkerboard pattern with each adjustment member spaced from another adjustment member by about 4 inches in order to permit access for an adjustment tool. When press bending apparatus is used to shape apertured glass sheets having one or more apertures located in a region of sharp bending, the adjustment members are usually not located in positions where critical adjustments may be made about the periphery of the critical apertures, which are most likely to be shaped out of tolerance limits. These apertures are needed in movable windows, such as side windows in automobile doors and the like, to receive actuating mechanisms that help open and close the windows.
U.S. Pat. No. 3,819,351 to Shaffer and Plank solves a need for providing means to adjust the critical portions of the shaping face of a press bending mold, namely, the portions that apply pressurized engagement against the peripheral portion of apertures in apertured glass sheets to be shaped by press bending. This patent provides means for locally adjusting the shaping face of a press bending mold in the vicinity of the periphery of any given aperture by providing a localized shape adjustment member in the vicinity of each aperture.
In a specific embodiment of the Shaffer and Plank patented apparatus, an aperture is provided in the relatively flexible metal plate in each region facing an aperture drilled through the glass sheet to be shaped by press bending, a metal plug having the same heat capacity per unit area as that of the metal plate and an area substantially coextensive with that of the aperture is supported within said aperture by a plug attachment member adjustably secured to the rigid member to which the attachment means of the Seymour patent adjustably secure the relatively flexible metal plate.
Each plug has its shaping surface conforming exactly to the shape desired for the bent glass sheet surrounding the given aperture. When the position of the plug attachment is properly adjusted, the plug attached thereto provides more precise control of the shape imparted to the glass sheet in the vicinity of a given aperture than is possible with the adjustment means provided by the apparatus of the aforesaid Seymour patent. Unfortunately, the plugged Shaffer and Plank patented apparatus produced press bent apertured glass sheets at yields below those experienced in press bending non-apertured glass sheets. These lesser yields were believed to be associated with fissures around the apertures of the apertured glass sheets.
U.S. Pat. No. 3,960,535 to Hamilton and Oelke reduces production losses in bending apertured glass sheets that are shaped while supported on an outline mold by using the outline mold to lift individual glass sheets into engagement against an upper mold of complementary shape. Each apertured portion of the glass sheet is provided with supplemental heat while supported on the outline mold to improve the temper of the resulting glass sheet and also to improve the survival rate of the shaped sheets processed through a cooling area of tempering apparatus immediately after shaping. The use of a horizontally disposed outline mold to support the hot glass sheet for shaping results in loss of control of sag in the intermediate portion of the glass sheet. Yet, an outline mold is needed to allow gas burners to radiate supplemental heat locally toward the vicinity of the apertured portions of the glass sheet being shaped. Furthermore, the inclusion of gas burners complicates the bending mold structure and introduces an additional complicating factor of coordinating the activity of the local gas burners with the operation of the shaping apparatus. The glass sheet bending art found it desirable to obtain a more simple apparatus to shape apertured glass sheets more closely to their desired shapes while providing an improved survival rate during the tempering process and less frequent breakage during processing after fabrication and during ultimate use of the fabricated product when installed.